Originally Posted by stevetech

P1637 is a little more serious CAN Bus error. The CAN Bus is the major electrical artery between major computer modules - ECM, TCCM, ABS, BPM, etc. The possible causes could be several, but some common possibilities - defective cabling/harnessing on the CAN, module to module, shorts, opens between modules, or defective programs/modules. P1637 finds a fault between the ABS/TCCM and the ECM, so you want to physically inspect these circuits, but could also be a corrupted program, diagnostics corrupted, or bad module(s), etc.

My first approach and simplest would be to clear the code, see if it repeats, then if it does, begin diagnosing from there. Sometimes the startup diagnostics in one of these modules hiccups and will set the code.